This invention is related to systems for calibrating the flow rate of fluid through a pump and more particularly to a calibration system for use in conjunction with a blending system utilizing a pump for injecting highly offensive and pollutant fluids which must be prevented from escaping into the atmosphere.
In some systems used in industrial processes today, the flow rate of a particular material through a line is determined primarily by the pump which is moving the material through the line instead of by controls responsive to a flowmeter. In such systems, it is necessary to calibrate this pump often to be assured that the flow rate being produced by the pump is that which is expected. One such system which requires such a calibration system is that which is disclosed in the copending patent application entitled "Component Injection System", Ser. No. 556,026, filed Mar. 6, 1975, by Lerner and Mayer. This component injection system is often used to control the injection of mercaptan or similar odorant substances into a stream of gas, such as propane, so as to provide an odor to the gas. Because of the viscous nature of mercaptan, and the low flow rates at which it is used, it is extremely hard to measure the flow rates and control it with normal metering and valve systems. Therefore, in this system a diaphragm pump is used to circulate the mercaptan around in a closed loop at a predetermined pulsed pumping rate, and then the loop is opened to a line connected to the mainstream of gas to be odorized, for a predetermined length of time at periodic intervals determined upon the flow rate of the mainstream. Therefore, to assure that the correct amounts of mercaptan are being injected into the mainstream, it is important to frequently calibrate the pump.
Under the old system, the calibration procedure has been quite an involved process due to the inherent characteristics of mercaptan. It has been the practice to completely clean out the entire lines of the injection system with a rinsing gas such as propane, so as to minimize the possibility of escape of mercaptan into the atmosphere. Then calibration of the pump is then accomplished by using a less volatile fluid. The pump is operated for a predetermined length of time and the amount of fluid which is pumped during this time is collected in an open container. Obviously, calibration of the injection system in this manner is a long drawn out process which results in extended down time for this system and still does not completely eliminate the possibility of air pollution.